This invention relates to a fiber optic device and more particularly to a device for dispersing light propagating along an optical fiber into an approximately uniform cylindrical pattern surrounding the fiber, and a method to manufacture this device.
During the course of the last several years, a new method of treatment for cancer in humans has been receiving considerable attention. Known as "photodynamic therapy" (PDT), this treatment makes use of two well-documented effects to destro cancerous tissues. The two effects are: (1) the propensity of certain chemicals to concentrate (or to remain) preferentially in cancer cells, and (2) the ability of light with a specific wavelength to promote photochemical reactions which, in the absence of such light, would proceed extremely slowly or not at all. The first effect is the foundation of the entire field of chemotherapy in which more or less "poisonous" chemicals are introduced into the patient. It is desired that lethal doses of the chamical concentrate in the cancer cells while non-lethal doses are received by normal cells. The second effect underlies the entire field of photochemistry in which light promotes many reactions not otherwise occurring. The fields of photography, photosynthesis, vision, etc. are common examples of light causing chemical reactions to proceed.
PDT combines these two effects in the treatment of cancer. A mixture of chemicals known as "hematoporphyrin derivative" (HpD) is widely known to remain preferentially in cancer cells. As extracted from serum, HpD fluoresces when exposed to light. This has proven to be a valuable diagnostic tool for many kinds of cancer. However, it has also been observed that, when illuminated with light of a specific wavelength and in sufficient intensity, HpD undergoes a photochemical reaction and kills the cell in which it resides. The exact nature of the chemical reaction which leads to the death of the host cell is not precisely defined and is the subject of continuing research at many institutions. However, the effect of killing the host cell is well-documented and is finding increasing use as a cancer treatment in the U.S. and elsewhere.
In clinical use, a patient is injected with HpD in an appropriate dosage as determined by the attending physician. The HpD permeates cells throughout the body, but dissipates from normal cells much more rapidly than from cancer cells. Typically, 48 to 72 hours after injection, HpD will remain in the patient's cancerous cells in much greater concentrations than in the surrounding normal tissue. Thus, exposing the cancerous region during this sensitive period to suitable light (for HpD this is red light with wavelength close to 630 nanometers) of sufficient intensity (as determined by the physician considering such things as the depth of the tumor, its nature, location, orientation etc.) will lead to preferential destruction of the cancerous tissues exposed to light.
PDT has several attractive features. HpD by itself is not a "poison". Thus, unlike much conventional chemotherapy, the patient has virtually no discmforting side effects from the treatment. (However, the patient is overly sensitive to light and is advised to stay out of sun light for several weeks following treatment.) PDT does not interfere with other modes of treatment. It can be readily used as part of a whole range of treatments the physician may prescribe for the patient. Most attractive of all, PDT is the first definite example of a method of cancer treatment combining photochemistry with preferential concentration in cancer cells. Since both effects are known to be widespread, HpD will almost certainly not be the last treatment to work in this manner.
However, some problems remain with PDT. The treatment is not effective unless suitable intensity of light is brought to bear upon the tumor. Thus, for cancers that rapidly spread over great areas, rapidly invade tissues deeply, or otherwise cannot be reached with light, PDT may not be the method of choice for the physician.
The present invention concerns a device which allows the physician to effectively deliver intense light to certain tumor sites not otherwise conveniently reached. The device must be capable of carrying intense radiation without overheating and destroying itself. The device must provide a uniform pattern of illumination so the physician can irradiate the entire treatment area with intense radiation lethal to the cancer cells, without leaving "dark areas" of undestroyed cells to cause future problems for the patient.
For cancers occurring in tubular regions of the body, the appropriate pattern of radiation for treatment is a uniform cycylindrical pattern. Thus, for PDT treatment of esophogeal cancer, an optical fiber is required to be equipped with an apparatus at one tip that disperses light propagating along the fiber in a uniform cylindrical pattern. This optical radiating apparatus must produce a reasonably uniform pattern of light, so the physician can have reasonable confidence in his applied dosage level. The apparatus must also be able to transmit reasonably intense radiation for effective treatment without developing "hot spots", optical, thermal or mechanical damage. Finally, the apparatus must perform these tasks in an environment in which it encounters blood, mucus, extraneous bits of tissues, and other substances which may contaminate its optical properties. Such an optical radiating apparatus for producing a uniform cylindrical pattern of light, and a method for manufacturing such an apparatus, is the subject of the present invention.
There have been a few other approaches to the problem of producing a uniform cylindrical pattern of intense light around the tip of an optical fiber. Work reported by Fujii et. al. in Optics and Laser Technology, February 1984, p. 40-44, considers the scattering of light from the tip of an optical fiber which has been subjected to various chemical etching and roughening procedures. While the patterns of light are measured precisely, they are far from uniform cylindrical patterns and not very useful in practical treatments.
Another approach to producing approximately uniform cylindrical patterns of light is that taken by the Quentron Optics Pty Ltd of Adelaide, Australia in their optical fibers marketed under the trade designation "QF-IA" and "QF-IV". The Quentron fiber has a light carrying core which is tapered to a point, allowing the propogating light to escape at each point along the tapered core. It is anticipated that the need to taper the core of the optical fiber will add substantially to the cost and complexity of manufacture.
The present invention comprises a coating for the tip of an optical fiber, and method of producing the coated tip, which produces an approximately uniform cylindrical pattern of light and requires no shaping of the fiber core.